Method of decreasing wax impregnation time by porous paper products

ABSTRACT

The rate at which a porous paper product absorbs molten paraffin waxes with a melting point less than 136* F. (AMP) is substantially increased by the addition of a small amount of an ester or mixture of esters of a fatty acid and a polyhydric alcohol to the wax before application.

United States Patent Kohn et a1. 1

1 51 Apr. 4, 1972 [54] METHOD OF DECREASING WAX IMPREGNATION TIME BY POROUS PAPER PRODUCTS [72] Inventors: Edward M. Kohn; Alexander D. Recchuite, both of Philadelphia, Pa.

[73] Assignee: Sun Oil Company, Philadelphia, Pa.

[22} Filed: Mar. 25, 1969 [21] Appl. No.: 810,120

[56] References Cited UNITED STATES PATENTS Schwartz et a1 ..ll7/158 X 3,194,677 7/1965 3,231,462 1/1966 Oswald et al... ..117/158 X 3,271,177 9/1966 Rumberger.... ..117/158 X 3,305,392 2/1967 Britt ..117/158 X 3,312,564 4/1967 Barbour... 17/158 X 3,332,798 7/1967 Kautsley 17/158 X 728,234 5/1903 Hoyt ..117/168 X 2,322,198 6/1943 Parsons... 117/168 UX 3,033,708 5/1962 McKee ..117/168 X 3,186,869 6/1965 Friedman. 17/168 X 3,229,010 l/1966 Carter 117/168 UX 3,433,665 3/1969 Harvey et a1. ..117/168 X Primary Examiner-William D, Martin Assistant Examiner-M. R. Lusignan Attorney-George L. Church, Donald R. Johnson and Wilmer E. Corgudale, Jr.

[5 7] ABSTRACT The rate at which a porous paper product absorbs molten paraffin waxes with a melting point less than 136 F. (AMP) is substantially increased by the addition of a small amount of an 2204612 6/1940 Musherm ""106/245 X ester or mixture of esters of a fatty acid and a polyhydric al- 2,483,259 9/1949 Badner et aL. 106/245 cohO] to the wax before application 3,061,456 10/1962 Davis et a1. ....1 17/158 X 3,177,091 4/1965 Case et a1 ..117/158 X 8 Claims, 1 Drawing Figure FOR LOW MELTING POINT WAXES l l I 1 I l WITHOUT ADDITIVE 1 WAX 1 WITH ADDITIVE 1 IMPREGNATION 1 TIME OF POROUS I I PAPER PRODUCTS, I SECONDS I T 1 1 I l O l l I O TMP Tx TBP lG-APPLICATION TEMPERATURE-J TEMPERATURE,F

Patented April 4, 1972 3,653,958

FOR LON MELTING POINT WAXES I I I I WITHOUT ADDITIVE I A 1 WITH ADDITIVE I IMPREGNATION I -w. I I TIME OFPOROUS I I I l I PAPER PRODUCTS, 1 g I SECONDS l T i I I I l I o I I I o- TMP Tx TBP k-APPLICATION TEMPERATURE l TEMPERATURE,F

INVENTORS EDWARD M. KOHN ALEXANDER D. RECCHUITE BY MEIMWIQ ATTORNEY METHOD OF DECREASING WAX IMPREGNATION TIME BY POROUS PAPER PRODUCTS BACKGROUND OF THE INVENTION The present invention provides a method for increasing the rate at which low melting point paraffin waxes will be absorbed by a porous paper product. This method produces an impregnated paper product in a substantially reduced amount of time thereby increasing the rate of product output of existing equipment.

Porous paper products, such as paperboard, corrugated paperboard, paper cupstock, are impregnated with paraffin waxes and the resulting wax-impregnated products are used for many purposes. In the manufacture of these wax-impregnated products it is necessary, because of competitive economic alternatives, that the system makes the product at the highest rate possible consistent with satisfactory product quality on existing equipment. This invention helps meet this requirement.

SUMMARY OF THE INVENTION The present invention provides a process by which the rate of absorption of molten paraffin waxes with a melting point less than 136 F. (AMP) by porous paper products is substantially increased over a wide range of impregnation temperatures. According to the invention, the increased paraffin wax impregnation rate is obtained by the addition of a small quantity of an ester or mixture of esters of a C -C fatty acid with a polyhydric alcohol having two to five carbon atoms and two to three hydroxyl groups to the wax and thereafter applying the mixture to the porous paper product.

BRIEF DESCRIPTION OF THE DRAWING The graph in the drawing plots wax impregnation time of porous paper products versus application temperature. This graph shows the effectiveness of the ester additive on the low melting wax impregnation time of porous paper products over a wide temperature range. Line 1 shows that the impregnation time of just wax is substantially independent of application temperature over a wide range, that is, between T p and T T is the boiling point of the wax. T is the temperature at which impregnation rate starts being related to the application temperature. T is between T and T The latter is the melting point of the wax. Thus between T and T impregnation time of just wax is dependent on application temperature whereas between T and T impregnation time of just wax is substantially independent of application temperature. Line 2 shows that the ester additive in the wax reduces the impregnation time over a wide temperature range. The dashed portion of line 2 indicates the anticipated rate improvement between the temperature range T and T DESCRIPTION In practicing the invention paraffin wax with a melting point less than 136 F., which is applied to the porous paper product, has incorporated into it a small amount of an ester or mixture of esters from a fatty acid and a polyhydric alcohol. The ester, used in this invention, can be a reaction product between a fatty acid having eight to 30 carbon atoms and a polyhdric alcohol containing two to five carbon atoms and two to three hydroxyl groups. Fatty acids refer to aliphatic monocarboxylic acids, both saturated and unsaturated, such as caprylic, n-nonadecylic, melissic, obtusilic, oleic, hiragonic, moroctic, stearolic, etc., but such acids as palmitic, stearic, oleic and linoleic are commercially available and therefore their esters are preferred in practicing the invention. Ethylene glycol, propylene glycol and glycerol are the preferred polyhydric alcohols; however, others such as l,4-butanediol; l,5-pentanediol; 1,2,4-butanetriol; pentanetriols; etc. can be used to prepare the ester additive.

A more specific group of the esters previously discussed are the glycerides, the manufacture of which is discussed in Kirk and Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Copyright 1965, 2nd Edition, Volume 8. A mixture of mono-, diand triglycerides is formed from the glycerol esterification of fatty acids. The maximum concentration of the monoglyceride in the mixture after removal of the reactants and by-products but without further processing is about 60 percent by weight. A monoglyceride fraction with a monoester concentration of about percent by weight can be obtained by molecular distillation. While a glyceride with a monoester content of about 90 percent by weight is used to illustrate the invention, lower monoester contents will work almost as well. The level of purity depends, in part, on whether the wax-coated article is intended to be used in contact with food.

When this invention is used to prepare a wax-impregnated paper product that will be in contact with food it is distinctly preferable that the fatty acid group of the glyceride, for example, be derived from an edible fat, since it will be harmless in case any of the monoglyceride seeps into the food product. An example of such monoglyceride is glycerol monooleate.

The glycerol monooleate or other ester as above specified is incorporated in the wax by mixing a small amount of it with molten wax. While the proportion of ester incorporated in the wax can range from about 0.005 to about 1.0 percent by weight, generally the range will be from about 0.01 to 0.50 percent by weight.

Many kinds of porous paper products can be impregnated with wax. Among these are paperboard, corrugated paperboard, kraft, sulfite and paper cupstock. The latter is used in the examples herein to demonstrate the principle of our invention.

Paraffin waxes are available with a wide range of physical properties, for example, melting point may be as low as F. or as high as F. (AMP). However, for reasons discussed hereinafter only paraffin waxes with melting points less than 136 F. (AMP) can be used in this process. The preferred melting point range of the wax is 100 to l35 F. (AMP).

The ester additive effect on wax impregnation rate by porous paper products depends on the type of wax and the melting point of the wax. Surprisingly the ester does not decrease wax impregnation time for all petroleum waxes. The ester does not affect the impregnation time of microcrystalline waxes. However, the ester affects waxes with a melting point less than 136 F. (AMP), for example a wax with a melting point of 127 F. (AMP), over a wide application temperature range.

The relative solubility of the ester in various waxes may explain why the ester works only with selected waxes. With low melting point waxes, the solubility of the ester in the wax is low over the entire temperature range considered practical for impregnation. Thus the ester, havinga low solubility in the wax, has a strong wetting influence on the porous paper when the wax-ester combination is applied to the paper product. On the other hand if the ester is highly soluble in the wax, such as the high melting point waxes used herein, it has no wetting influence on the porous paper products.

EXAMPLES Table I below lists some of the physical properties of the waxes which were used for illustrative purposes in the runs shown in Table II. A microcrystalline wax was included for comparative purposes.

Physical Properties Melting poinl,

"F. (AMP') 127 136 156 178 Viscosity. SUS at AMP is the American Melting Point which is 3 F. higher than the ASTM melting p011.

The paraffin wax was placed in a beaker and heated till its temperature was about F. above its melting point. The ester, in the desired amount, was added to the melted wax. One cubic centimeter of 'a suitable dye was added to every 1,000 of solution. The dye aided in the visual observations.

The ester used is glycerol monooleate. This monooleate had a minimum monoester content of 90.0 percent, saponification value of 155-165, iodine value 65-70, a maximum glycerol content of 1.5 percent (as oleic), a specific gravity of 0.95-0.96 at 40 C. and a melting point of 29 to 35 C.

The wax-ester-dye mixture was placed in a penetrometer. This instrument measures the time required for molten wax at a fixed temperature to impregnate a sample of paper product. About 700 cc. of wax are contained in a trough with a circular orifice on the upper surface. The cupstock was placed over the orifice and held there by a glass plate and clamp. The glass plate allows the operator to observe the test area of the cupstock.

The wax was brought into contact with the cupstock by tilting the trough down. This action activated a timer. When the operator saw that the cupstock was impregnated completely he tilted the trough up automatically stopping the timer.

Table 11 below lists the penetration data obtained with the penetrometer for the waxes mentioned in Table 1 when said waxes were mixed with the additive.

weight of additive 1 Percent weight of additive: Additive is defined in Examples.

The application temperature of Run 1 is in that temperature range where decreases in the temperature increase impregnation time. 1n the accompanying drawing the application temperature of Run 1 is within T to T range. Runs 2, etc., are in that range where changes in application temperature does not change impregnation time. In the heretofore mentioned drawing the application temperatures of Runs 2, etc. are within the T to T range.

Run 2 with a low melting point wax shows that at a 150 F. application temperature and with no additive the average impregnation time is 17.2 seconds. However with the 0.05 weight percent ester the average impregnation time is 15.5

seconds for a decrease in impregnation time of about 10 percent. Runs 3, 4 and 5, with the same low melting point wax, show that as the application temperature increases the ester always causes a decrease in the average impregnation time. Yet Run 6, with a higher melting point wax (136 F., AMP). shows that the ester additive has no effect on the average impregnation time. Runs 7 and 8, with an even higher melting point wax (156 F., AMP), shows the same lack of effect on impregnation time by the ester. A similar lack of ester effect on impregnation time is shown in Run 9 with a microcrystalline wax.

The average impregnation times shown in Table 11 are the arithmetic average of nine trials.

Runs 2, 3, 4 and 5 with no additive show impregnation times of 17.2, 16.4, 17.0 and 17.9 seconds respectively. Statistical analysis indicates that these lmpregnatlon times are equivalent. Statistical analysis also indicates that the impregnation rate differences for Runs 2, 3, 4 and 5 with and without additives are significant. The same statistical analysis indicates that the ester in the wax has no effect on impregnation rates in Runs 6, 7, 8 and 9.

While in these examples the outside of the cupstock was treated, the invention is equally applicable to treatment of the inside of the cupstock.

Substantially equivalent results, as in the above specific examples are obtained when (1) other low melting point 136" F., AMP) waxes are used and/or (2) other esters as herein specified are used including 'mono-, diand tri-esters of other C C fatty acids with C -C polyhydric alcohols having two to three hydroxyl groups or mixtures of such esters and/or (3) other porous paper products as herein specified are used.

The invention claimed is:

1. 1n the impregnation of porous paper with a molten paraffin wax having a melting point below 136 F. (AMP), the improvement which comprises utilizing as the impregnating composition said paraffin wax having incorporated therein from 0.01 to 1.0 percent by weight of an additive which is an ester or mixture of esters of a C -C fatty acid with a polyhydric alcohol having two to five carbon atoms and two to three hydroxyl groups, wherein said ester is a monoester or at least 60 percent by weight of said mixture of esters are monoesters, and impregnating the paper with said composition.

2. Method according to claim 1 wherein the paraffin wax melts between F. and F. (AMP).

3. Method according to claim 1 wherein the alcohol has two to three carbon atoms.

4. Method according to claim 1 wherein the paraffin wax contains a mixture of esters having about 90 percent by weight of a monoester.

5. Method according to claim 1 wherein the ester or mixture of esters is present in the wax in the amount of about 0.01 to 0.5 percent by weight.

6. Method according to claim 2 wherein the alcohol has two to three carbon atoms.

7. Method according to claim 6 wherein the paraffin wax contains a mixture of esters having about 90 percent by weight of a monoester.

8. Method according to claim 7 wherein the mixture of esters is present in the wax in the amount of 0.01 to 0.5 percent by weight. 

2. Method according to claim 1 wherein the paraffin wax melts between 100* F. and 135* F. (AMP).
 3. Method according to claim 1 wherein the alcohol has two to three carbon atoms.
 4. Method according to claim 1 wherein the paraffin wax contains a mixture of esters having about 90 percent by weight of a monoester.
 5. Method according to claim 1 wherein the ester or mixture of esters is present in the wax in the amount of about 0.01 to 0.5 percent by weight.
 6. Method according to claim 2 wherein the alcohol has two to three carbon atoms.
 7. Method according to claim 6 wherein the paraffin wax contains a mixture of esters having about 90 percent by weight of a monoester.
 8. Method according to claim 7 wherein the mixture of esters is present in the wax in the amount of 0.01 to 0.5 percent by weight. 